The present invention relates to a seat weight measuring apparatus for measuring a load applied on a vehicle seat such as the weight of a passenger sitting thereon. Particularly, it relates to a seat weight measuring apparatus which has been improved not to spoil the performance of load sensors due to dimensional error or deformation of a vehicle body or a seat and also improved to provide higher precision measurement.
Automobiles are equipped with seat belts and airbags to secure safety for passengers in the automobiles. In recent years, there is a trend for controlling the operation of such safety devices according to the weight (body weight) of a passenger for improved performance of seat belts and airbags. For example, the amount of gas to be introduced into the airbag, an airbag inflating speed, or a pre-tension of the seat belt may be adjusted according to the weight of a passenger. For that purpose, some means are needed for measuring the weight of the passenger sitting on the seat. An example of such means includes a proposal of an apparatus for measuring the weight of a passenger by the following steps of arranging load sensors (load cells) at four corners of the bottom of a seat, obtaining loads on the respective corners, and summing them to determine the seat weight including the weight of the passenger (Japanese Patent Application No. H09-156666, Japanese Patent Application No. H10-121627 filed by the applicant of this invention).
To make an accurate measurement by this seat weight measuring apparatus, it is necessary to eliminate loads besides the weight of the seat and the weight of the passenger (or an object) on the seat. One of loads needed to be eliminated is a load to be applied when the seat weight measuring apparatus is forced to be assembled despite the fact that the vehicle or the seat has dimensional error or deformation (in the specification, this load will be referred as to xe2x80x9cassembly loadxe2x80x9d).
To obtain a seat weight measuring apparatus which has good durability and high precision but can be manufactured at low cost, it is necessary to establish a strain detecting mechanism which amplifies small strains. Further, it is necessary to reduce manufacturing errors of parts in the mechanism of the apparatus and measurement errors due to the frictional force.
The present invention is made under the above circumstances and the object of the present invention is to provide a seat weight measuring apparatus which has been improved not to spoil the performance of load sensors due to dimensional error or deformation of a vehicle body or a seat.
A further object of the present invention is to provide a seat weight measuring apparatus which has been improved to attain high precision measurement.
Yet another object of the present invention is to provide a seat weight measuring apparatus which has good durability and high precision but can be manufactured at low cost.
To solve these problems, the seat weight measuring apparatus of the present invention is a seat weight measuring apparatus for measuring a seat weight including the weight of a passenger sitting thereon, which comprises: load sensors arranged inside a seat or between the seat and a vehicle body for converting at least parts of the seat weight into electric signals; and an absorbing mechanism for absorbing dislocation and/or deflection between the seat and the vehicle body.
The aforementioned absorbing mechanism is arranged on the connecting and holding portions between the load sensors and the seat or between the load sensors and the vehicle body to absorb dimensional errors, not to transmit an assembly load exerted due to manufacturing error of parts and/or dimensional dislocation, and/or deformation caused by the installation to the load sensors. Therefore, only pure load to be measured (seat weight) is applied to the load sensors, thereby enabling secure measurement using the effective ranges of the load sensors enough widely. It can also prevent a load exceeding the measurable range of the load sensors from being exerted.
It should be noted that the intention of the seat weight measuring apparatus as described in this specification is basically to measure the weight of a passenger sitting on a vehicle seat. Accordingly, an apparatus for measuring only the weight of a passenger by canceling the weight of a vehicle seat itself is also contained in the range of the seat weight measuring apparatus disclosed by this specification.
According to the present invention, it is preferable that the absorbing mechanism works even after the seat weight measuring apparatus is installed in the vehicle body and the seat.
Even when an unexpected load is exerted on the seat and the seat thus deforms after the seat weight measuring apparatus is installed in the vehicle body or the vehicle body deforms while the vehicle runs, such deformation can be absorbed by connecting portions not to be transmitted to the load sensors.
In the seat weight measuring apparatus of the present invention, it is preferable that the absorbing mechanism includes a slide mechanism and a pivotal mechanism.
Positional, dimensional, and rotational dislocation can be absorbed.
The seat weight measuring apparatus of the present invention preferably further comprises a centering mechanism for regulating the position of the absorbing mechanism.
The centering mechanism is composed of, for example, a relatively weak spring and causes the slide mechanism or the pivotal mechanism to be positioned as close to the center in the slidable range or the pivotal angle as possible. By the function of the centering mechanism, the movement of the slide mechanism and the pivotal mechanism after the installation of the seat weight measuring apparatus can be secured in the both directions (right and left, up and down, forward and backward).
The seat weight measuring apparatus according to another aspect of the present invention is a seat weight measuring apparatus for measuring a seat weight including the weight of a passenger sitting thereon, comprising load sensors arranged inside a vehicle seat or between the seat and a vehicle body for receiving load (including moment, hereinafter referred as to xe2x80x9capplied loadxe2x80x9d) relating to the seat weight and for converting the applied load into electric signals, characterized in that each of the load sensors has a cantilever-type sensor member which is deformable when subjected to the applied load, and a plurality of strain gauges attached to one surface (strain measuring surface) of the sensor member; and that the load sensor is so structured that one of the strain gauges is subjected to tensile strain while other one of the strain gauges is subjected to the compressive strain when the sensor plate is subjected to the applied load and thus deformed.
The strain gauge to be subjected to tensile strain and the strain gauge to be subjected to compressive strain are wired on a bridge circuit in such a manner as to form an opposite phase, thereby increasing the outputs of the strain gauges. This attains highly precise measurement with small strains on the sensor, thereby increasing the life of the sensor.
Because the surfaces on which the strain gauges are attached are on one side of the sensor member (e.g. one side of a plate), printing process should be made only on one side when the strain gauges and wirings are printed by, for example, screen printing. This allows sensors to be manufactured at lower cost.
The seat weight measuring apparatus according to another aspect of the present invention is a seat weight measuring apparatus for measuring a seat weight including the weight of a passenger sitting thereon, comprising load sensors arranged inside a vehicle seat or between the seat and a vehicle body for receiving load relating to the seat weight and for converting the load into electric signals, characterized in that each of said load sensors has a sensor member of which thickness is constant and width is partially different and which is deformable when subjected to the applied load, and a plurality of strain gauges attached to one surface (strain measuring surface) of the sensor member; that the strength in deformation of an elastic deforming portion of the sensor member is adjusted so as to form a region providing substantially constant surface strain on a portion of the strain measuring surface of the sensor member when the sensor member is subjected to the applied load; and that the strain gauges are attached to that region.
Since the strain gauges are attached (printed) on the region providing substantially constant surface strain, the strains may not vary even though the positions of the strain gauges are slightly shifted, thereby preventing measurement error. Therefore, this can ensure high precision of measurement and can reduce the quality requirement on manufacturing.
The seat weight measuring apparatus according to another aspect of the present invention is a seat weight measuring apparatus for measuring a seat weight including the weight of a passenger sitting thereon, comprising load sensors arranged inside a vehicle seat or between the seat and a vehicle body for receiving load relating to the seat weight and converting the load into electric signals, characterized in that each of the load sensors has a sensor member of which thickness is constant and width is partially different and which is deformable when subjected to the applied load, and a plurality of strain gauges attached to one surface (strain measuring surface) of the sensor member; that the sensor member is a cantilever; that one end is a fixed portion, the other end is a subjected portion to be subjected to the applied load, and a portion between the ends is a strain gauge fixing portion; and that both the fixed portion and the subjected portion are patched with reinforcing members to concentrate strain in the strain gauge fixing portion.
Because strains are concentrated in the portion on which the strain gauges are attached, highly precise measurement is performed and measurement error can be prevented even with manufacturing error and/or assembling error of other parts.
According to this aspect, it is preferable that the subjected portion of said sensor member is provided with a half arm, wherein the half arm has a body having relatively high rigidity to be in contact with the subjected portion and wings projecting the body, wherein said wings have action portions to be subjected to simple load (normal load not moment), wherein said half arm has such a structure (reversing structure) that the simple load is transmitted mainly as bending moment to the subjected portion of said sensor member via the body of said half arm, and wherein according to the reversing structure of said half arm, a wave-like strain is applied to the strain measuring surface of said sensor member.
Further, it is preferable that said half arm is provided with a releasing mechanism at the action points thereof, wherein the releasing mechanism releases load besides vertical load by sliding or rotation, and that the strain gauge fixing portion of said sensor member has a compression-side region and a tension-side region which are arranged symmetrically about a neck portion with a reduced width in its plane view.
When load is applied in the longitudinal direction and/or rotational moment is applied, the balance of strain between the tension side and the compression side is changed in such a manner as not to change the total sensitivity of the sensors relative to the vertical load. Even with dislocation in a horizontal direction (e.g. the longitudinal direction of the vehicle) or axial force acting on the sensor plate, error can be cancelled by means of the compression-side strain gauge and the tension-side strain gauge and the total sensitivity obtained by summing the outputs of both the strain gauges may not include such error.
In the seat weight measuring apparatus of the present invention, it is preferable that the action points of said half arm and the center line in the thickness of the sensor member are set to be in substantially the same level or have height difference of xc2x15 mm or less. That is, when frictional force (axial force) acts on the aforementioned action points, the moment arm for deforming the sensor plate due to the frictional force is short. This means that the deformation of the sensor plate due to the frictional force is little, thereby reducing the measurement error.